Bruce Nazarian, M.P.S.E. has put together a great FAQ for feature film audio post. It's a very thorough overview that covers everything from THX to M&E.
Ever since silent movies began to talk, filmmakers have been looking to control and improve the quality of the sound of their creation. As soon as creators realized there was a way to control and enhance the sound of their pictures, Audio Post was born, and has been a fact of life ever since.
Link to the FAQ, via gnomemedia.com.